Surgical sutures are well known medical devices in the art. The sutures may have braided or monofilament constructions, and may be provided in single-armed or double-armed configurations with a surgical needle mounted to one or both ends of the suture, or may be provided without surgical needles mounted. The sutures are used in a variety of conventional medical and surgical procedures to approximate tissue, affix or attach implants to tissue, etc. Surgical sutures may be made from a variety of known bioabsorbable and nonabsorbable materials. For example, sutures are known to be made from aromatic polyesters such as polyethylene terephthalate, nylons such as nylon 6 and nylon 66, polyolefins such as polypropylene, silk, and other nonabsorbable polymers. In addition, sutures may be made from polymers and copolymers of p-dioxanone (also known as 1,4-dioxane-2-one), ε-caprolactone, glycolide, L(−)-lactide, D(+)-lactide, meso-lactide, trimethylene carbonate, and combinations thereof. Of particular utility is polydioxanone homopolymer.
Surgical sutures are typically available in a range of conventional sizes for a variety of conventional surgical procedures. The size of the suture used by the surgeon for any particular procedure is dictated in part by the type of tissue to be sutured, the relative size of the tissue structure, as well as the forces that will be applied to the sutures by the approximated tissue after the surgical procedure has been completed. Similarly, the type of suture selected will be dictated by the procedure. Nonabsorbable sutures are typically used for applications such as cardiovascular, vascular, orthopedic, gastrointestinal and the like wherein a nonabsorbable suture is desired or required because a permanent or an extended period of fixation is required during the healing period, e.g., implantation of a heart valve prostheses. Bioabsorbable sutures are typically used for applications such as plastic surgery, skin fixation and certain soft tissue approximation, and the like. A bioabsorbable suture may be used when extended tissue approximation or fixation is not required as long as the suture maintains adequate strength during the healing period, and it is desirable to replace the suture with autologous tissue such as skin or soft tissue during the healing process.
In certain applications where significant tensile forces will be applied on a suture, it is desirable to use materials that will provide high tensile strength with minimal suture size or cross-section. The tensile strength of a suture is known to be a function of several parameters including material, suture size, filament diameter, type of construction (i.e., braided versus monofilament), ratio of sheath to core in a braided construction, type of material in the core, etc. In particular it is known to use ultra high molecular weight polyethylene (hereinafter referred to as UHMWPE) to construct sutures. Sutures made from ultra high molecular polyethylene have the advantage of having high tensile strength while having a smaller suture size. A disadvantage of such sutures is that ultra high molecular weight polyethylene is a relatively slippery material. This inherent slipperiness may affect the knot integrity of a suture. In a typical surgical procedure, after the surgeon makes multiple passes of the suture through tissue so that it is properly approximated and stitched, one or more conventional knots are placed in the suture by the surgeon to maintain the suture in place and thereby prevent it from loosening. Loosening of a suture may allow the approximated tissue to split apart, thereby compromising the surgical procedure and preventing healing with the potential for causing catastrophic effects (e.g., anasotomosis graft blow out in cardiovascular repairs, implant dislodgement, organ failure, soft tissue dislocation from a bone, etc.).
In order to improve the knot holding characteristics (e.g., knot strength) of ultra high molecular polyethylene sutures, it is known to combine the ultra high molecular weight polyethylene yarn component with another yarn component that has surface friction higher that the ultra high molecular weight yarn component. For example it is known to provide a ultra high molecular weight polyethylene suture having an nonabsorbable core, an ultra high molecular weight polyethylene core or an aromatic polyester core with an outer sheath surrounding the core braided from a combination of ultra high molecular weight polyethylene fiber yarns and yarns made from fibers of a nonabsorbable material such as an aromatic polyester. It is also known to have a suture that has a nonabsorbable ultra high molecular weight polyethylene core or an aromatic polyester core surrounded by an outer braided sheath braided from a yarn made from ultra high molecular weight polyethylene fibers and a yarn made from fibers of a bioabsorbable polymer.
Although such composite ultra high molecular weight polyethylene sutures provide increased tensile strength, there are several disadvantages associated with their use. One disadvantage is the possibly diminished knot characteristics that they provide. Typically such sutures produce a large knot having increased mass, size and/or volume. A knot in a nonabsorbable suture remains in the patient's body after the tissue has been approximated and the healing has been completed, and may irritate soft tissue and cause patient discomfort and pain. It is known that from a medical perspective it is desirable to minimize the mass of an implant in tissue. In addition, it is advantageous for an implant to allow for autologous tissue migration or in-growth to provide for better healing. A bioabsorbable implant such as an absorbable suture permits tissue ingrowth as the mass of the implant is resorbed or degraded by the patient's body to provide for better healing. This healing process allows the patient's tissue to assume the tissue loads as the absorbable portion of the implant or suture resorbs/degrades and loses structural integrity and strength. The ultra high molecular weight polyethylene sutures of the prior art have a dense nonabsorbable volume and knot mass, even when combined with a bioabsorbable component, which for the most part remains behind after the tissue healing process has occurred, contributing to problems discussed above.
Accordingly, what is needed in this art are novel composite sutures constructed from materials providing high tensile strength, and bioabsorbable materials, wherein the composite sutures provide optimal tensile strength with minimal mass of high tensile strength material, and have good knot strength and knot security, and reduced in vivo knot profile over time, while allowing tissue ingrowth.